13.5V constant ouput OR regular voltage regulator???

The reason you're having a hard time getting a consistent answer is that people keep piping up with wrong information stated as "fact" but with no real-world basis, just what they think they remember of what they understood of what they read awhile back.

"Constant output" is a misleading name for this regulator. All ordinary voltage regulators regulate (i.e., keep constant) the line voltage in the running automobile. There's no such thing as a magical regulator that can overcome Ohm's Law -- by which I mean that when the alternator is producing less than 13.5v because engine RPMs are low and electrical demands are high, the regulator cannot magically cause the line voltage to be 13.5v. In fact, the "constant output" regulator is nothing more or less than a regular regulator with its mounting bracket plastic-coated to insulate it from ground. This has the effect of full-fielding the alternator so line voltage goes way up with engine revs. This can give you a stronger spark for a very short time before things start getting damaged, so it really, really is a race-only item (and kind of a dumb one). You're far better off with a regular regulator. The MP resto regulator looks nifty, but the quality of the electronics is poor (same with MP ignition boxes!). Call up Ray at Old Car Parts Northwest for a NOS genuine Mopar regulator.